Ojeda G., Mattana S., Avila A., Alcaniz J.M., Volkmann M., Bachmann J. (2015) Are soil-water functions affected by biochar application?. Geoderma. 249-250: 1-11.LinkDoi: 10.1016/j.geoderma.2015.02.014
Today biochar is considered a stable-carbon source that is able to improve soil quality. However, although biochar effects on some soil properties are already becoming well known, its impact on complex soil hydrological functions has yet to be better assessed. The main objectives are: (a) to determine the impact of different biochar amendments on important physical and chemical soil properties and (b) to determine whether the origin (biomass or sewage sludge) and pyrolysis technique can change biochar properties and regulate biochar influence on important soil functions, i.e. nutrient release, water sorption, and carbon storage. Six types of biochar produced from different biomass sources (pine, poplar or sludge) and pyrolysis processes (slow, fast or gasification) were applied to a sandy-loam, low-organic-matter, calcareous soil (mean dose: 18. g/kg) and incubated in a greenhouse without seeding. Two sampling campaigns, one month and one year after biochar amendments, were performed. The overall impact of biochar, analysed by principal response curves (PRCs), indicated that it could improve or deteriorate soil hydrological properties at different intensities. Soil wettability was modified due to sludge biochar addition to soil by increased water penetration dynamics during the capillary rise process of about 18%. In contrast, water storage as a soil function during soil drying was not affected. Because no differences on aggregate stability were observed between treatments, increments on soil organic carbon could not be related to biochar physical protection caused by aggregate formation or by enhanced aggregate stability. As a result, carbon storage, considered as a soil function provided by biochar, was mainly related to its chemical stability. On the other hand, nutrient flux during soil slaking was improved, increasing nutrient release from soil to water. In terms of biochar properties, an increment of surface wettability of biochar during water drop penetration was observed after one year of its addition to soil, where the mean values of contact angle (CA) decreased 69.5%. This important result suggest that initial biochar hydrophobicity (CA. >. 90°) disappeared after 1. year. It was observed that PRC analysis was able to identify important key soil properties that should be monitored when biochar is used as soil amendment. We conclude that the impact of biochar on soil functions depends mainly on biochar feedstock rather than on the pyrolysis technique used during its production. In general, the performance of biochar obtained from sludge and vegetal biomass was markedly different. © 2015 Elsevier B.V.
Ojeda G., Mattana S., Alcañiz J.M., Marando G., Bonmatí M., Woche S.K., Bachmann J. (2010) Wetting process and soil water retention of a minesoil amended with composted and thermally dried sludges. Geoderma. 156: 399-409.LinkDoi: 10.1016/j.geoderma.2010.03.011
Composting or thermally-drying sludges are becoming commonly used in soil rehabilitation of degraded land. Sludge amendments increase soil organic matter, but can reduce soil wettability due to hydrophobic compounds. The main objective of this study is to analyse how composted and thermally dried sludges influence soil wettability and water retention properties of a minesoil obtained from limestone extraction during quarrying rehabilitation activities. Three composted (Blanes, Manresa and Vilaseca) and three thermally dried (Besós, Mataró and Sabadell) municipal sludges from different wastewater plants of medium-sized towns located in Catalonia (NE Spain) were mixed with a minesoil and filled into lysimeters The minesoil water retention curves and, the time required for their measurement were analyzed together with various soil key parameters. Throughout the wetting process, three characteristic points of the water retention curve were identified: (i) the air soil dryness point corresponding to a soil suction of - 25 MPa, (ii) the critical point where high suction regime changes to low suction regime, located around - 6 MPa and (iii) the wilting point, corresponding to a soil suction of - 1.5 MPa. One month after sludge amendments (S1), two composted sludges increased the vapour wetting time corresponding to wilting point (twp) of minesoil, while 1 year after sludge amendments (S2) two thermally dried sludges decreased twp. On the other hand, all composted sludges and one thermally dried sludge increased minesoil water retention corresponding to wilting point (wwp) at sampling one (S1), while at sampling two (S2) similar effects were observed except in one composted sludge treatment. Regarding to soil biophysical properties, the addition of composted and thermally dried sludges to minesoil increased total organic carbon, soil-water contact angle, microbial biomass, pH and electrical conductivity at both experimental time scales (S1 and S2), while extractable carbohydrates was only modified at S1. The sludge effects on soil wetting properties and biophysical parameters were dependent on sewage sludge origin and the type of post-treatment. Increases in total organic carbon, extractable carbohydrates, contact angle, microbial biomass or electrical conductivity and decreases in pH corresponded with increases in twp and wwp. It was observed that under similar conditions of water vapour adsorption, minesoil amended with composted sludge could have more difficulties to overcome the permanent wilting point under wetting process. © 2010 Elsevier B.V. All rights reserved.
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